The frequency band used in communication devices such as mobile phones or wireless LANs (Local Area Networks) range from several hundred MHz to several MHz and it is required that the communication devices have high efficiency for wide band in the frequency band. Therefore, on the precondition that the antenna used for these devices is adapted to function as a high gain antenna operating in the band described above, it is further requested that, particularly, the antenna is small in size and short in height from the viewpoint of its use situation. Moreover, in the case of digital terrestrial broadcasting developed recently, it is necessary that the antenna to be used therein covers a wide frequency band such as 470 MHz to 770 MHz being now used as a television broadcasting band in Japan. Further, in digital broadcasting, for example, a band of 180 MHz to 210 MHz is being used in Korea and a band of 470 MHz to 890 MHz is being used in Europe. Accordingly, the advent of an antenna is expected which can be used in a band of frequencies being 180 MHz or more and also can be small in size and short in height so as to be mounted in communication devices such as mobile phones. Furthermore, in not only an antenna but also an electronic device such as a personal computer and a personal digital assistant, a signal transmission speed is made higher and a driving frequency is also made higher and, as a result, various kinds of inductance element to be used therefor have to be suitably corresponded to the high frequencies.
Conventionally, as a small-sized antenna suitably used in mobile communications, a chip antenna using a dielectric ceramic has been provided (for example, Patent Reference 1). With the frequency falling within a constant level, by using a dielectric of higher permittivity, the chip antenna can be made smaller in size. In the Patent Reference 1, an attempt is made to shorten a wavelength by using a meander electrode. Also, another antenna is proposed in which the miniaturization of an antenna is achieved by using a magnetic material having not only a higher relative permittivity εr but also higher relative permeability μr to shorten a wavelength by 1/(εr·μr)1/2 times (see Patent Reference 2).
In the case where an antenna or inductance element is made of a magnetic material, for example, in the case where spinel ferrite such as Ni—Zn ferrite is used as the magnetic material, there was a limitation to the use in high frequency regions due to a phenomenon of so-called “Snoek's limit”. To solve this problem, hexagonal ferrite is proposed as one of magnetic materials for an antenna which can maintain, owing to its direction of easy magnetization appearing within a plane being vertical to a C axis, its specified permeability until a frequency band exceeds a frequency limit (Snoek's limit) of the spinel ferrite (see Patent Reference 3). The Patent Reference 3 discloses that the Z-type ferrite, most grains of which have a single magnetic domain structure, can be effectively used in high frequency band in particular.    Patent Reference 1: Japanese Patent Application Laid-open No. Hei10-145123.    Patent Reference 2: Japanese Patent Application Laid-open No. Sho 49-40046.    Patent Reference 3: International Publication No. 96/15078 brochure.